1. Field of the Invention
The present invention relates to an image forming apparatus, an image forming system and a control method.
2. Description of Related Art
In an image forming apparatus using an electrophotographic scheme, a cleaning device of a blade-cleaning type has been used in which a plate-shaped cleaning blade composed of an elastic body and serving as a device for removing remaining toner such as untransferred toner and transfer residual toner on an image bearing member is brought into contact with the surface of an image bearing member to remove the remaining toner on the image bearing member, for example.
In recent years, reduction of the particle size of the toner of image forming apparatuses of an electrophotographic scheme has been demanded from the view point of enhancing the image quality, and for such a purpose, polymerization methods such as the emulsion polymerization method and the suspension polymerization method have been utilized, for example. As the size of the toner particle decreases, however, the attaching force between the toner particle and the image bearing member increases, thus reducing the ease of removal of the remaining toner on the image bearing member. In particular, when a so-called polymerization toner produced by a polymerization method is used, the toner particles have a substantially spherical shape, and as a result cleaning failures in which the toner particles roll on the image bearing member and slip through the cleaning blade is easily caused, thus further reducing the ease of removal of the remaining toner on the image bearing member. In addition, when toner slips through the cleaning blade, the toner becomes the core of toner aggregate formed on the image bearing member, and grain blank (grain noise) is generated on the solid image printing part.
To solve such a quality problem as the “slipping” and “grain noise,” today, lubricant-external additive (hereinafter referred to as “lubricant”) is supplied onto the image bearing member such that cleaning is performed in the state where the attaching force between the toner particles and the image bearing member is reduced to a low level. Examples of the approach for supplying lubricant onto the image bearing member include a lubricant application process in which lubricant is scraped with a brush to supply the lubricant to the surface of the image bearing member; and a toner adding process in which a toner image is formed with toner containing lubricant to supply the lubricant.
The toner adding process does not require a coating device such as a lubricant rod and a brush and therefore is advantageous in terms of installation space and cost. In the toner adding process, however, the lubricant is preferentially consumed when an image having a low area rate is continuously printed, and as a result, the amount of the lubricant in the developing device decreases. When the amount of the lubricant in the developing device decreases, the amount of the lubricant supplied to the surface of image bearing member may decrease, and a region where no lubricant is supplied may be formed. Consequently, reduction of the adhesion to toner which is a purpose of supplying lubricant to the image bearing member cannot be achieved, and cleaning failure may occur.
In particular, for the purpose of preventing the above-mentioned problems, a patch image (toner image) is formed in regions other than the image region on the image bearing member when an image having a low area rate is formed. By forming the patch image, lubricant is supplied onto the image bearing member, and the toner in the developing device is consumed, and as a result, new toner is supplied into the developing device. When the new toner is supplied, lubricant is also supplied, and thus the amount of the lubricant in the developing device can be prevented from being reduced, and in turn, the amount of the lubricant on the image bearing member can be prevented from being reduced.
For example, Japanese Patent Application Laid-Open No. 2014-145864 discloses a technique in which a patch image between images is formed based on the gradation information of the image, and lubricant is selectively supplied to the regions where cleaning failure may possibly occur.
However, the toner used for patch image formation for supplying lubricant to the image bearing member is discarded as it is without being transferred to sheets. Consequently, as a large number of patch images are formed, the consumption amount of the toner increases, and the cost for supplying lubricant onto the image bearing member disadvantageously increases.